Electrical devices are commonly used for various medical diagnosis and treatment purposes. One such use is the use of electrodes to carry electric currents to a patient (also referred to herein as a user) for different purposes. Electrodes are conductors through which an electric current can enter or leave a medium. In the medical field, electrodes have been used in part with, for example, defibrillators, electrocardiography (“EKG”), electroencephalography (“EEG”), and iontophoresis.
Iontophoresis is a non-invasive method of propelling high concentrations of a charged substance, known as the active agent, transdermally by repulsive electromotive force using a small electrical charge. The active agent can include a drug or other therapeutic agent for example, insulin, iron containing compounds, chemotherapeutic agents, etc. The charge is applied by an electrical power source (also referred to herein as an electrical current source) to an active electrode assembly placed on the skin which contains a similarly charged active agent and a solvent in which it is dissolved. Current flows from the electrode assembly through the skin and then returns by means of a return or counter electrode assembly also placed on the skin. A positively charged electrode assembly, termed the anode will repel a positively charged active agent, or anion, into the skin, while a negatively charged electrode assembly, termed the cathode, will repel a negatively charged active agent, known as a cation into the skin.
When the electrode assemblies are placed on the skin, the electric field lines from the electrode assemblies go through the skin. This causes a large amount of electric field crowding near the edges of the electrodes and leads to a higher current density along the edges of the electrode along with ohmic heating of the edges and/or skin in electrical contact with the edges due to the higher current density. This phenomenon is known as edge effect. As a result, when a sudden amount of current is passed to the electrodes, the edges of the electrodes may heat and cause burns or other thermal injury on the user's skin. Therefore, there is a need for electrode assemblies that distribute current density more evenly so that the edge effect and the accompanying heating produced by the edge effect may be reduced.